Project Summary/Abstract Men who have sex with men (MSM) are the population most affected by HIV in the United States, accounting for over two-thirds of all new HIV diagnoses. Pre-exposure prophylaxis (PrEP) has demonstrated high levels of efficacy for HIV prevention among MSM, however, discontinuation rates are high and are emerging as the primary challenge in implementing PrEP. A pharmacy-led model of PrEP delivery, combined with mobile app-based PrEP support, could address many of the challenges with starting and staying on PrEP, and also greatly reduce burden on the medical system, as the current requirement for quarterly clinic visits would require 4.4 million additional medical visits annually. Based on the Information-Motivation-Behavioral Skills model, we have developed the PrEP-3D intervention, an integrated mobile app to increase PrEP uptake and persistence among MSM, with key features including 1) a sexual risk score that incorporates the impact of PrEP use on risk; 2) an integrated sexual and pill-taking diary that provides information on levels of PrEP protection based on adherence patterns, augmented with pill reminders and motivational badges; 3) an interactive bi-directional messaging support system with automated check-ins to allow rapid resolution of issues such as side effects or insurance issues; and 4) integration with an online pharmacy-led PrEP program that coordinates lab tests and medication refills, provides medication support, and addresses insurance/cost issues. The effectiveness of this integrated PrEP-3D platform will be compared with clinic-based PrEP provision among MSM initiating PrEP throughout the San Francisco Bay Area (SFBA), a highly diverse region ranking 2nd in the number of new HIV diagnoses in California. In aim 1, PrEP-3D will be refined through iterative focus groups with 32-40 MSM, followed by optimization of the intervention in a 3-month technical pilot among 30 MSM, 10 of whom will be Spanish-speaking. In aim 2, we will conduct a randomized controlled trial to evaluate the effectiveness of PrEP-3D in improving PrEP initiation and persistence in the SFBA. In this trial, we will enroll 150 at-risk MSM interested in starting PrEP who will be randomized 2:1 to PrEP-3D (N=100) or a standard of care control condition (clinic-based PrEP delivery) (N=50) and assess tenofovir-diphosphate (TFV- DP) levels in dried blood spots at 3, 6, 9, and 12 months as our primary outcome measure. In aim 3, we will assess cost and cost-effectiveness of PrEP-3D vs. clinic-based PrEP delivery. To ensure inclusion of those disproportionately impacted by HIV in the SFBA, we will enroll at least 50% Black and Latino and 50% under age 35. These studies will test the hypotheses that the PrEP-3D intervention will be more effective than clinic- based PrEP delivery in increasing PrEP uptake and persistence among MSM, and can serve as a scalable model for expanding PrEP services and support to vulnerable populations nationwide.